1. Field of the Invention
The present invention relates to a method for producing a semiconductor element and a cleavage apparatus for use in the method.
2. Description of the Related Art
A conventional method for producing a semiconductor element (e.g., a semiconductor laser element) will be described with reference to FIGS. 5A through 5C. Initially, a semiconductor multi-layer structure 11 is provided as a semiconductor wafer 1 by successively laminating a plurality of semiconductor layers including an active layer. A plurality of grooves 15 to be used for cleavage (hereinafter referred to as cleavage grooves) are provided on the front surface of the semiconductor multi-layer structure 11 along a longitudinal direction of the cavity of a semiconductor laser element (direction X in FIG. 5A). The grooves 15 are evenly spaced and parallel to each other. The active layer is provided about 4 xcexcm below the front surface of the semiconductor multi-layer structure 11.
Thereafter, a stripe-patterned electrode 13 is provided on the entire front surface of the semiconductor multi-layer structure 11 excluding the cleavage grooves 15. A back electrode 12 is provided on the entire back surface of the semiconductor multi-layer structure 11. The wafer 1 is cut into rectangles. A plurality of short scratches are provided at an edge of the rectangular semiconductor multi-layer structure 11 along the longitudinal direction of the cavity of a semiconductor laser element (direction X). The scratches are evenly spaced as shown in FIG. 5A.
Thereafter, the integral of the semiconductor multi-layer structure 11, the patterned electrode 13, and the back electrode 12 is cleaved (first cleavage) in a direction perpendicular to the cleavage grooves 15 provided between the stripes of the patterned electrode 13, using the scratches 14 as starting points of cleavage. Thereby, a plurality of multi-element bars 16 are obtained. The multi-element bar 16 has the back electrode 12a on the entire back surface of he bar-shaped semiconductor multi-layer structure 11 and plurality of patterned electrodes 13 separated by the cleavage grooves 15 on the front surface of the bar-shaped semiconductor multi-layer structure 11 as shown in FIG. 5B.
Thereafter, referring to FIG. 5C, each multi-element bar 16 is cleaved (second cleavage) along the cleavage grooves 15, resulting in a plurality of semiconductor laser elements 17. Each semiconductor laser element 17 has the patterned electrode 13 on the front surface of the semiconductor multi-layer structure 11 and the back electrode 12a on the back surface of the semiconductor multi-layer structure 11. When a voltage is applied between the patterned electrode 13 and the back electrode 12a, laser light is emitted from a facet produced by the first cleavage.
The cleavage grooves 15 are, for example, scratches (grooves) formed mechanically by a diamond needle of a scriber or the like. In this case, there is a micro crack extending from the cleavage groove 15 inward the semiconductor multi-layer structure 11. The micro crack reduces the strength of crystal. Therefore, when a load is applied from the back electrode 12a side to the cleavage groove 15 provided on the multi-element bar 16, the multi-element bar 16 is easily cleaved along the micro crack having a lesser crystal strength. In order to conduct the second cleavage to the multi-element bar 16 on which the cleavage grooves 15 (scratches) are provided, a relatively small load is applied to the back electrode 12a in a longitudinal direction of the multi-element bar 16. For example, a load is applied to the back electrode 12a by a roller being rotated and moved on the back electrode 12a. 
Japanese Laid-Open Publication No. 6-338662 discloses a method for forming scratches (grooves) as the cleavage grooves 15 on a semiconductor wafer in which semiconductor laser elements are provided. When the cleavage grooves 15 are formed mechanically used a scriber or the like, a plurality of cleavage grooves 15 need to be reliably provided from one edge to the other edge of the patterned electrode 13. Such a process reduces working efficiency.
Further, the semiconductor wafer 1 is easily broken along the scratches which is being formed on the semiconductor wafer 1. Breaks also easily occur along the scratches during the first cleavage in a direction perpendicular to the scratches. As a result, a yield of the semiconductor laser elements is lowered.
To address the above-described problems, the cleavage grooves 15 may be provided by etching. In this case, the front surface of the semiconductor wafer is first coated with a resist film, excluding portions thereof in which the cleavage grooves 15 will be provided. Such portions which has not been covered with the resist film are etched, resulting in the cleavage grooves 15 having a V-shaped cross-section as shown in FIG. 7. In such a process, all the cleavage grooves 15 are formed at once. Therefore, the working efficiency of production of the cleavage grooves 15 is improved as compared with when the cleavage grooves 15 are formed mechanically using a scriber or the like as described above.
Japanese Laid-Open Publication No. 62-137894 discloses a cleavage apparatus 2 shown in FIG. 6. In the cleavage apparatus 2, etched grooves are provided as the cleavage grooves 15 on the multi-element bar 16. The multi-element bar 16 is placed on a film 31, and a sheet 34 is provided on the multi-element bar 16. Further, the sheet 34 is covered with a film 32. Thereafter, a load is applied via the film 31 to the multi-element bar 16 using a roller 33 so that the multi-element bar 16 is cleaved.
As described above, when the cleavage grooves 15 (etched grooves) are formed by etching, substantially no micro crack is generated inside the semiconductor multi-layer structure 11 unlike the scratches mechanically provided using a diamond needle or the like. Therefore, portions having low strength are not clearly provided inside the semiconductor multi-layer structure 11. Therefore, when the multi-element bar 16 is subjected to the second cleavage, a greater load is required as compared with when the multi-element bar 16 has the cleavage grooves 15 mechanically formed. In this case, the multi-element bar 16 cannot be reliably cleaved (second cleavage) when a load applied by the roller 33 is relatively low.
In particular, in the apparatus 2, the multi-element bar 16 is sandwiched by a pair of the films 31 and 32, and is further held by a ring, thereby providing tension for the film 31. A load is applied to the multi-element bar 16 using the roller 33. Therefore, when the tension of the film 31 is changed, the load applied to the multi-element bar 16 is likely to be changed. Moreover, the film 31 or the multi-element bar 16 may be displaced due to the pressure caused by the roller 33. The above-described reasons makes it difficult to apply a constant load to the multi-element bar 16. It is also difficult to rotate the roller 33 smoothly while applying a constant load to the multi-element bar 16 sandwiched by a pair of the films 31 and 32.
As described above, it is difficult to cleave the multi-element bar 16 sandwiched by a pair of the films 31 and 32 by applying a constant load to the multi-element bar 16.
Japanese Laid-Open Publication No. 54-93356 discloses a cleavage method in which the cleavage grooves 15 having a V-shaped cross-section is formed by etching, and the insides of the cleavage grooves 15 are subjected to rough surface treatment, thereby providing micro cracks inside the semiconductor multi-layer structure 11; and thereafter, by rotating a roller, a load is applied to a surface (back surface) of the multi-element bar 16 opposite the surface on which the cleavage groove 15 are provided so that the multi-element bar 16 is cleaved (second cleavage). In such a method, the strength of the cleavage grooves 15 can be clearly distinguished from the strength of portions in which the cleavage grooves 15 are not provided. Therefore, a small load applied to the back surface causes the second cleavage in the multi-element bar 16.
However, in this case, the rough surface treatment is required after the cleavage grooves 15 have been provided by etching, thereby reducing working efficiency. Moreover, when the cleavage grooves 15 are subjected to the rough surface treatment, micro cracks are accidentally generated in portions other than the insides of the cleavage grooves 15. The semiconductor multi-layer structure 11 may be broken at such portions.
Further, when the multi-element bar 15 is subjected to the first cleavage, the semiconductor multi-layer structure 11 is likely to be broken along the cleavage grooves 15 which are deep.
According to one aspect of the present invention, a method for producing a semiconductor element comprises the steps of: forming a plurality of grooves on a first surface of a semiconductor multi-layer structure along a first direction; forming a plurality of multi-element bars by cleaving the semiconductor multi-layer structure along a second direction; placing at least one of the plurality of multi-element bars on a support stage; and cleaving the at least one of the plurality of multi-element bars along the plurality of grooves by moving a pressure member in a longitudinal direction of the at least one of the plurality of multi-element bars while a constant load is applied by the pressure member to a second surface of the at least one of the plurality of multi-element bars, the second surface being opposite a third surface corresponding to the first surface of the at least one of the plurality of multi-element bars.
In one embodiment of this invention, the semiconductor multi-layer structure includes an active layer.
In one embodiment of this invention, the first direction is orthogonal to the second direction.
In one embodiment of this invention, the plurality of grooves are formed by etching.
In one embodiment of this invention, the multi-element bar is placed on the support stage via a support sheet.
In one embodiment of this invention, the support sheet includes polyvinyl chloride.
In one embodiment of this invention, the constant load is applied by the pressure member to the at least one of the plurality of multi-element bars via a protection sheet.
In one embodiment of this invention, the protection sheet includes a polyethylene terephthalate sheet, a surface of which is to be in contact with the pressure member is coated with a silicone resin.
In one embodiment of this invention, the support stage includes a rigid material.
In one embodiment of this invention, the rigid material includes at least one of a quartz, a glass, a metal, a stone, and a rigid plastic.
In one embodiment of this invention, a depth of the plurality of grooves is about 0.5 xcexcm or more and about 5 xcexcm or less from the first surface.
In one embodiment of this invention, a moving speed of the pressure member is about 10 mm/sec or more and about 100 mm/sec or less.
In one embodiment of this invention, the constant load applied to the at least one of the plurality of multi-element bars is about 5 N or more and about 20 N or less per multi-element bar.
According to another aspect of the present invention, a cleavage apparatus is provided for producing a semiconductor element using at least one multi-element bar, a plurality of grooves being provided in a predetermined direction on a first surface of the at least one multi-element bar. The apparatus comprises: a support stage for the at least one multi-element bar being provided; and a pressure member for applying a constant load to a second surface of the at least one multi-element bar, the second surface being opposite the first surface of the at least one multi-element bar, while the pressure member is moved in a longitudinal direction of the at least one multi-element bar.
In one embodiment of this invention, the at least one multi-element bar includes an active layer.
In one embodiment of this invention, the plurality of grooves are formed by etching.
In one embodiment of this invention, the support stage includes a rigid material.
In one embodiment of this invention, the rigid material includes at least one of the quartz, a glass, a metal, a stone, and a rigid plastic.
In one embodiment of this invention, a moving speed of the pressure member is about 10 mm/sec or more and about 100 mm/sec or less.
In one embodiment of this invention, the constant load applies to the at least one multi-element bars is about 5 N or more and about 20 N or less per multi-element bar.
In one embodiment of this invention, the pressure member does not rotate on the at least one multi-element bar.
In one embodiment of this invention, the pressure member is held by a spring, and the constant load is applied by the spring to the at least one multi-element bar.
Thus, the invention described herein makes possible the advantages of providing a method for producing a semiconductor element and a cleavage apparatus, in which a multi-element bar having shallow cleavage grooves formed by etching is efficiently and reliably cleaved into a plurality of semiconductor elements.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.